ON THE FORMATION OF CRYSTALLINE ROCKS. 259 



§ 5. — Uuiidd ju'ocess. 



The action of the vapor of ^\•ater on the chlorides and on the sili- 

 cates, which has just been noticed, is, as it were, an intermediate 

 one between the dry and the wet way. It remains for us to sum 

 up the results of thi.s last. Bequerel has long ago shown the influ- 

 ence of slow action, aided by electricity of very feeble tension, in 

 precipitating insoluble combinations which imitate those of nature.* 

 It was also by the slow decomposition of silicic ether that Ebelmen 

 produced a hj^drated silica in solid, compact masses, similar to hyalite 

 and hydrophane.f Gustave Rose has skilfully analyzed the condi- 

 tions under which carbonate of lime is precipitated in the state of 

 arragonite. Bischof and Sterry Hunt have made divers experi- 

 ments, the first to verify his ideas on the formation of minerals, the 

 second in support of his theory of the origin of magnesian rocks.:]: 

 Charles Deville has examined how it is that water, Avith the sole 

 aid of carbonic acid, and without the help of pressure, can contribute 

 to the formation of dolomites. § From reactions which are produced 

 in the manufacture of hydraulic limes and cements, Kuhlmann has 

 deduced interesting results for geology. II Mention may here be made 

 of the action of the alkalies on rocks, by Delesse.H It is especially 

 at high temperatures and under pressure that we succeed in imitating 

 mineral substances in water. 



Hall** and Cagniard-Latourft long ago discovered that vegeta- 

 bles in these conditions are affected in a peculiar manner. By sub- 

 mitting wood in water to a temperature of about 300° centigrade, I 

 produced a real anthracite. || At a lower temperature Baroulier, 

 by means of vegetables enclosed in moist clay, obtained an imitation 

 of coal.§§ 



The beautiful experiment of Haidinger and Morlot on the formation 

 of dolomite has inaugurated the use of w^ater under pressure for the 

 formation of minerals. Ilil Instead of forming dolomite by the reaction 

 of sulphate of magnesia on carbonate of lime, Favre and Marignac 

 have since used the chloride of magnesium to produce the same 

 effect. •Ill 



De Senarmont has undertaken a long series of experiments, 



« Annaks de Chimie ei de Physique, vol. xxxii, p. 244, 1823. 

 •f Annales des Mines, 4th series, vol. viii, p. 149; Cowptes Rendus, vol. xxi, p. 527; 

 LeonJiard's Jarbuch, p 807, 1858. 



■^ Biblioiheque de Geneve, 1857, p. 268. 



§ Comptes Rendus, vol. xlvii, p. 90, 1858. 



II Comptes Rendus, vol. xii, p. 852 ; vol. xxxv, p. 739. 



^ Bulktin de la Sociede Giologique, 2d series, vol. xi, p. 127. 



■"-« Hall obtained a kind of coal by the dry way. 



ft Comptes Rendus, vol. xxxii, p. 275, 1857. 



XX Annales des Mines, 5th series, vol. xii, p. 305, 1857. 



§§ Comptes Rendus, vol. xlvi, p. 376, 1858. 



fill Mimoirea de V Acadtmie de Vienne, vol. 1, p. 305, 1847. 



^^ Bibliotheque de Geneve, May, 1849. 



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